Method for Recovering Hydrocarbons from Subterranean Formations

ABSTRACT

Recovery of viscous hydrocarbon from subterranean formations is assisted by using a plurality of novel U-tube type wells, each with dual wellheads, a moveable wellbore packer, a lateral section with a concentric communication zone and with sequential injection production perforations in which heat is injected into the proximal perforations and hot oil and produced fluids are produced from the distal perforations, the whole process being controlled by modulating the production flow where the wellbore fluids are controlled to act as a hydraulic seal to limit bypass of injected fluids. The injection-production displacement process moves axially along the wellbore in a sequential manner as hydrocarbon volumes are depleted by injected fluid displacement of oil and oil and water production.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority from provisional application 60/712,289filed Aug. 30, 2005 and Disclosure Document 521,535 by Dr. HenryCrichlow.

INTRODUCTION

This invention relates generally to a new technology application and anew type of oil well for recovery of viscous hydrocarbons fromsubterranean oil bearing formations. The technology involves the noveluse and application of equipment and techniques in which horizontalwells are drilled from the surface down to and across an oil bearingformation and back up to the surface, in a manner similar to that ofdrilling under a river crossing when laying pipelines across country.This new type of horizontal well is called a Uniwell™ because it has twosurface wellheads one at each end of the axis of the horizontal system.Either wellhead can be used for either injection or production as neededby the operator.

The technology is a new application using some elements of an existingtechnology, which has hitherto been used in horizontal pipeline crossinginstallations and some technology elements, which have been used inconventional oil well drilling.

FIELD OF THE INVENTION

THIS INVENTION is a unique new approach to drilling horizontal wells foroil recovery. The invention is particularly suited to making heavy oilformations and tar sands producible by a single wellbore drilled using aspecialized form of horizontal directional drilling. The inventionhowever is not limited to recovery of heavy oils only; it can be usedfor many oil recovery processes such as tar sands and oil shale.

With this invention, the operator can drill a new type of well that hasall the operational benefits of a horizontal well and in addition thisdrilling can be implemented either by using modified equipment that isreadily available in allied industries such as pipeline laying or bymodifying existing oil well drilling rigs. This novel drilling approacheffectively lowers costs and increases efficiencies because it canutilize available equipment to drill wells with greater productivecapacity. This approach allows wells to be drilled over large lateraldistances, up to as much as 5,000 feet in shallow depth oilfields. Atgreater depths the lateral extension is limited by the rig capabilityand mechanical limitations of torque and drag in the drilling process.With this innovation, in field practice, which involves in part, theinjection and production from the same well, albeit at different ends ofthe horizontal axis, increased levels of oil recovery are achievable. Itis also possible to produce from the same wellhead by using concentrictubular strings and allowing the produced fluid to be removed from thesame wellhead.

BACKGROUND OF THE INVENTION

Introduction:

Heavy hydrocarbons in the form of petroleum deposits are distributedworldwide and the heavy oil reserves are measured in the hundreds ofbillions of recoverable barrels. Because of the relatively high oilviscosity which can exceed 10⁶ Cp, these crude deposits are essentiallyimmobile and cannot be easily recovered by conventional primary andsecondary means. The only economically viable means of oil recovery isby the addition of heat to the oil deposit, which significantlydecreases the viscosity of the oil by several orders of magnitude andallows the oil to flow from the formation into the producing wellbore.Today, the steam injection can be done in a continuous fashion orintermittently as in the so-called “huff and puff” or cyclic steamprocess. Oil recovery by steam injection involves a combination ofphysical processes including, gravity drainage, steam drive and steamdrag to move the heated oil from the oil zone into the producingwellbore.

The most significant oil recovery problem with heavy oil, tar sands andsimilar hydrocarbonaceous material is the extremely high viscosity ofthe native hydrocarbons. The viscosity ranges from 10,000 cp at the lowend of the range to 5,000,000 cp at reservoir conditions. The viscosityof steam at injection conditions is about 0.020 cp. Assuming similarrock permeability to both phases steam and oil, then the viscosity ratioprovides a good measure of the flow transmissibility of the formation toeach phase. Under the same pressure gradient, gaseous steam cantherefore flow from 500,000 to 250,000,000 times easier through thematerial than the oil at reservoir conditions. Because of this viscosityratio, it is imperative and critical to any recovery application thatthe steam be confined or limited to an area of the reservoir by a seal.This seal can be physical, hydraulic or pneumatic and essentially mustprovide a physical situation which guarantees no-flow of any fluidacross an interface. This can be implemented by several means. Withoutthis “barrier” the steam will bypass, overrun, circumvent, detour aroundthe cold viscous formation and move to the producer wellbore. Thisinvention addresses and resolves this major obstructive element in heavyoil recovery.

Horizontal wells have played a prominent part in recovery of oil. Thesewells can be as much as 4 times as expensive as conventional verticalwells but the increased expense is offset by the increased rates of oilproduction and faster economic returns. Several patents have describedvarious approaches to using horizontal wellbores. The need forhorizontal wells requires a more efficient economical and easilydeployable system for developing and drilling these horizontal wells.This novel utilization proposed herein addresses the needs and teaches amethod of horizontal well drilling and a production mechanism that ismore easily implemented, allows a larger portion of the reservoir to beexposed and allows more oil recovery to occur.

By implementing the new processes which are taught in this applicationby this invention the oilfield operator can see improved performance,lower costs, better oilfield management, and allow for efficient andorderly development of petroleum resources.

Improvements have been made in enhancing the contact of the steam withthe native heavy oil by the introduction of horizontal well technology,which allows greater recovery than with the customary vertical wells.This current invention provides a further extension of the horizontaltechnology in which a novel drilling methodology is applied to thedrilling effort to allow wells of much larger lateral extent,potentially larger diameters and thereby more efficient recoverysystems. This invention also describes the use of the single wellbore asthe injection and production system simultaneously without the need foradditional concentric or multiple complicated tubular systems in thewell.

No fully operational cases of horizontal drilling with two wellheadshave been reported in the oil and gas drilling industry. To date,horizontal directional drilling with two wellheads, i.e. with an entryand exit wellhead, has been a technology limited almost exclusively tothe pipeline construction industry in which the engineers routinely usethe horizontal directional drilling techniques to cross rivers bydrilling a horizontal well from one side of the river bank, several feetunder the river bottom and across to the other bank. Refs.1 and Ref. 2are horizontal directional drilling publications, which show exampleswhere this technology has been successfully used in river crossings likethe Chinese Yangtze River where the crossing was 5,538 feet laterallyand 170 feet below the ground level. Some environmental uses havedeveloped recently in which horizontal wells are drilled under immovablestructures like buildings to allow liquid contaminants to be siphonedoff or produced from subsurface layers.

Prior Art:

Various methods and processes have been disclosed for recovery of oiland gas by using horizontal wells. There have been various approachesutilized with vertical wellbores, to heat the reservoirs by injection offluids and also to create a combustion front in the reservoir todisplace the insitu oil from the injection wellbore to the productionwellbore.

Wilson in U.S. Pat. No. 5,165,491 provides a mechanism for putting moreweight on the drill bit by utilizing the weighted heavy drill collars inthe general vertical portion of the well such that the maximum weightcomponent is available on the bit.

U.S. Pat. No. 5,467,834 provides the method and apparatus for drillingthe curved portion of a horizontal well by using a flexible compositedrill pipe. U.S. Pat. No. 6,202,761 further elaborates on the process ofdrilling the initial curved portion of the wellbore by placing a windowturning shoe and drilling out a window through the casing.

Keller in U.S. Pat. No. 5,803,666 indicates a process to allow a pilothole to be back-reamed in making a horizontal crossing with an invertedliner to support the wall of the wellbore.

Landers in WO 99/66168 describes a drilling apparatus for horizontalwells using a horizontal cutting jet blaster device under very highhydraulic pressure. U.S. Pat. No. 5,934,390 by Uthe discusses a similarjet drilling approach.

Rozendaal in patent application US2002/0066598 A1 discloses a reamingdevice which allows the pilot hole drilled by horizontal drillingmachines used in underground utilities for gas, water, electric andphone lines to be reamed to a larger diameter.

U.S. Pat. No. 6,357,537 illustrates the typical use of conventionalhorizontal directional drilling equipment and the drilling process. Thispatent and others like it show the use of the drilling technologylimited to shallow utility type crossings.

Rankin et al. in patent US2002/0096362 A1 describe a back-reamer deviceused to enlarge a pilot hole. This device is steer-able and allows theback-reaming process to maintain correct alignment.

Balton in U.S. Pat. No. 5,402,851 teaches a method wherein multiplehorizontal wells are drilled to intersect or terminate in closeproximity to the vertical well bore. The vertical wellbore is used toactually produce the reservoir fluids. The horizontal wellbore providesthe conduits, which direct the fluids to the vertical producingwellbore.

Butler et al in U.S. Pat. No. 4,116,275 use a single horizontal wellborewith multiple tubular strings internal to the largest wellbore for steamrecovery of oil. Steam was injected via the annulus and after a soakperiod the oil is produced from the inner tubing strings.

U.S. Pat. No. 5,626,193 by Nzekwu et al disclose a single horizontalwell with multiple tubing elements inside the major wellbore. Thishorizontal well is used to provide gravity drainage in a steam assistedheavy oil recovery process. This invention allows a central injectortube to inject steam and then the heated produced fluids are producedbackwards through the annular region of the same wellbore beginning atthe farthest or distal end of the horizontal wellbore. The oil is thenlifted by a pump. This invention shows a method where the input andoutput elements are the same single wellbore at the surface.

U.S. Pat. No. 5,215,149 Lu, uses a single wellbore with concentricinjection and production tubular strings in which the injection isperformed through the annulus and production occurs in the inner tubularstring, which is separated by a packer. This packer limits the movementof the injected fluids laterally along the axis of the wellbores. Inthis invention the perforations are made only on the top portion of theannular region of the horizontal well. Similarly the production zonebeyond the packer is made on the upper surface only of the annularregion. These perforated zones are fixed at the time of well completionand remain the same throughout the life of the oil recovery process.

Huang in U.S. Pat. No. 4,700,779 describes a plurality of parallelhorizontal wells used in steam recovery in which steam is injected intothe odd numbered wells and oil is produced in the even numbered wells.Fluid displacement in the reservoir occurs in a planar fashion.

U.S. Pat. Nos. 6,951,247, 6,929,067, 6,923,257, 6,918,443, 6,932,155,6,929,067, 6,902,004, 6,880,633, 20050051327, 20040211569 by variousinventors and assigned to Shell Oil Company have provided a veryexhaustive analysis of the oil shale recovery process using a pluralityof downhole heaters in various configurations. These patents utilize amassive heat source to process and pyrolize the oil shale insitu andthen to produce the oil shale products by a myriad of wellboreconfigurations. These patents teach a variety of combustors withdifferent geometric shapes one of which is a horizontal combustor systemwhich has two entry points on the surface of the ground, however thehydrocarbon production mechanism is considerably different from thoseproposed herein by this subject invention.

Shell U.S. Pat. No. 6,953,087 shows that heating of the hydrocarbonformation increases rock permeability and porosity. This heating alsodecreases water saturation by vaporizing the interstitial water. Thecombination of these changes increases the fluid transmissibility of theformation rock in the heated region.

U.S. Pat. No. 6,948,563 illustrates that increases in permeability mayresult from a reduction of mass of the heated portion due tovaporization of water, removal of hydrocarbrons, and/or creation offractures. In this manners fluids may more easily flow through theheated portion.

U.S. Pat. No. 3,994,341 teaches a vertical closed loop system inside thewellbore tubulars in which a vertical wellbore is used to generate avertical circulation of hot fluids which heat the wellbore and nearbyformation. Hot fluids and drive fluids are injected into upperperforations which allow the driven oil to be produced from the bottomof the formation after being driven towards the bottom by the drivefluid.

U.S. Pat. No. 6,7255,922 utilizes a plurality of horizontal wells todrain a formation in which a second set of horizontal wells are drilledfrom and connected to the first group of horizontal wells, These wellsfrom a dendritic pattern arrangement to drain the oil formation,

U.S. Pat. No. 6,729,394 proposes a method of producing from asubterranean formation through a network of separate wellbores locatedwithin the formation in which one or more of these wells is a horizontalwellbore, however not intersecting the other well but in fluid contactthrough the reservoir formation with the other well or wells.

U.S. Pat. No. 6,708,764 provides a description of an undulating wellbore. The undulating well bore includes at least one inclining portiondrilled through the subterranean zone at an inclination sloping towardan upper boundary of the single layer of subterranean deposits and atleast one declining portion drilled through the subterranean zone at adeclination sloping toward a lower boundary of the single layer ofsubterranean deposits. This embodiment looks like a waveform situated inthe rock formation.

U.S. Pat. No. 5,167,280 teaches single concentric horizontal wellboresin the hydrocarbon formation into which a diffusible solvent is injectedfrom the distal end to effect production of lowered viscosity oilbackwards at the distal end of the concentric wellbore annulus.

U.S. Pat. No. 5,655,605 attempts to use two wellbores sequentiallydrilled from the surface some distance apart and then to have thesewellbores intersect each other to form a continuous wellbore with twosurface wellheads. This technology while theoretically possible isoperationally difficult to hit such a small underground target, i.e theaxial cross-section of a typical 8-inch wellbore using a horizontalpenetrating drill bit. It further teaches the use of the horizontalsection of these intersecting wellbores to collect oil produced from theformation through which the horizontal section penetrates. Oilproduction from the native formation is driven by an induced pressuredrop in the collection zone by a set of valves or a pumping system whichis designed into the internal concentric tubing of this invention. The5,655,605 patent also describes a heating mechanism to lower theviscosity of the produced oil inside the collection horizontal sectionby circulating steam or other fluid through an additional central tubinglocated inside the horizontal section. At no time does the steam orother hot fluid contact the oil formation where viscosity lowering byheat transfer is needed to allow oil production to occur.

U.S. Pat. No. 4,532,986 teaches an extremely complex dual well systemincluding a horizontal wellbore and a connecting vertical wellbore whichis drilled to intersect the horizontal well. The vertical well containsa massively complex moveable diverter system with cables and pulleysattached to the two separate wellheads to allow the injection of steam.This system is used to inject steam from the vertical wellhead into thehorizontal wellbore cyclically and sequentially while the oil isproduced from the wellhead at the surface end of the horizontal well.

U.S. Pat. No. 4,037,658 teaches the use of two vertical shafts or wellsconnected by a cased horizontal shaft or “hole” with a flange in thevertical well. This type of downhole flange connection is extremelydifficult if not impossible to implement in current oilfield practice.Two types of fluids are used in this patent, one inside the horizontalshaft as a heater fluid and one in the formation as a drive fluid. Bothfluids are injected either intermittently of simultaneously from thesurface wellheads. The laboratory demonstration in this patent showsthat the annular steam zone is very conductive to oil production andallows premature steam breakthrough. Based on this demonstratedobservation, it is difficult if not impossible, to conceive a situationtaught by this patent in which the injected steam as drive fluid willnot preferentially flow under the hundreds of pounds injection pressurealong the heated annular zone and thus bypassing the cold viscous oilsaturated formation. It is noted that the cold viscous formation has analmost zero mobility. This patent essentially teaches a system in whichthe injected steam shall be cycled through the horizontal tube and theannular zone in the formation under field conditions providing little ifany sweep efficiency.

U.S. Pat. No. 3,986,557 claims a method using a horizontal well with twowellheads that can inject steam into a tar sand formation mobilizing thetar in the sands. In this patent, during the injection of the steam itis hoped that the steam will enter the formation and not continuedirectly down the open wellbore and back to the surface of the oppositewellhead. It is difficult to visualize the steam entering a cold highlyviscous formation while a highly open wellbore is available for fluidflow away from the formation. Furthermore, U.S. Pat. No. 3,986,557teaches that the steam is simultaneously injected through perforationsinto the cold bitumen formation while hot oil is flowing through thesame perforations, in the opposite direction through the rock porestructure, against the invading high pressure steam. This situation isnot only physically impossible but it thermodynamically impossible forthe hot fluid to flow “against the pressure gradient”.

U.S. Pat. No. 4,445,574 teaches the drilling of a single well with twowellheads. This well is perforated in the horizontal section and aworking fluid is injected into the wellbore to produce a mixture ofreservoir oil and injected working fluid. Similar to the U.S. Pat. No.3,986,557 patent it is difficult from a hydraulic point of view tovisualize and contemplate the working fluid entering the formation whilean open wellbore is available for fluid flow horizontally and verticallyout the distal end of this wellbore.

U.S. Pat. No. application 20050045325 describes a recovery mechanism forheavy oil hydrocarbons in which a pair of wells is used. A verticalinjector well is horizontally separated from a vertical production well.The hot fluid, steam or air is injected into the bottom portion of theinjector and is expected to displace the very viscous immobile oil fromthe cold reservoir and push this hot oil through the cold oil saturatedformation eventually to the producer. The invention expects oil flow tooccur by drilling a web or radial channels from the injector to theproducer. It is inconceivable that viscous cold oil, or even lowerviscosity hot oil will preferably flow along these channels whileextremely low viscosity high-pressure steam will flow through the coldformation. Flow in porous media dictates that hot, saturated steam willcompletely bypass cold viscous oil and the process will be a quick steamrecycle process from injector to producer.

Ref. 4, the Society of Petroleum Engineers (SPE), 222 Palisades CreekDr., Richardson, Tex. 75080, U.S.A, publishes several hundred papers onheavy oil recovery.

SPE paper 37115 describes a single-well technology applied in the oilindustry which uses a dual stream well with tubing and annulus: steam isinjected into the tubing and fluid is produced from the annulus. Thetubing is insulated to reduce heat losses to the annulus. Thistechnology tries to increase the quality of steam discharged to theannulus, while avoiding high temperatures and liquid flashing at theheel of the wellbore.

SPE paper 78131 published an engineering analysis of thermal simulationof wellbore in oil fields in western Canada and Calif., U.S.A.

SPE paper 53687 shows the production results during the first year of athermal stimulation using dual and parallel horizontal wells using theSAGD technology in Venezuela.

SPE paper 50429 presents an experimental horizontal well where thehorizontal well technology was used to replace ten vertical injectionwells with a single horizontal well with limited entry. Thelimited-entry perforations enabled steam to be targeted at the coldregions of the reservoir.

SPE paper 75137 describes a THAI—‘Toe-to-Heel Air Injection’ systeminvolving a short-distance displacement process, that tries to achievehigh recovery efficiency by virtue of its stable operation and abilityto produce mobilized oil directly into an active section of thehorizontal producer well, just ahead of the combustion front. Air isinjected via a separate vertical or a separate horizontal wellbore intothe formation at the toe end of different horizontal producer well andthe combustion front moves along the axis of the producer well.

SPE paper 50941 presents the “Vapex” method which involves injection ofvaporized hydrocarbon solvents into heavy oil and bitumen reservoirs;the solvent-diluted oil drains by gravity to a separate and differenthorizontal production well or another vertical well. S

PE paper 20017 teaches a computer simulation of a displacement processusing a concentric wellbore system of three wellbore elements andcomplex packers in which steam is injected in a vertical wellboresimilar to that in the U.S. Pat. No. 3,994,341 patent. Simulated steaminjection occurs through one tubing string and circulates in thewellbore from just above the bottom packer to the injection perforationsnear the top of the tar sand. This perforations near the top of the tarsand. This circulating steam turns the wellbore into a hot pipe whichheats an annulus of tar sand and provides communication between thesteam injection perforations near the top of the tar sand and the fluidproduction perforations near the bottom of the tar sand. This processrequires 7 years to increase oil production from 20 BOPD to 70 BOPD.

SPE paper 92685 describes U-tube well technology in which two separatewellbores are drilled and then connected to form a single wellbore. TheU-tube system was demonstrated as a means of circumventing hostilesurface conditions by drilling under these obstacles.

SPE 76727 describes that steam displacement in an undergroundhydrocarbon reservoir occurs because of three components driving oilproduction. These are gravity drainage, steam drag and steam drive.Gravity drainage is caused by the oil column height and the differencein density between the hot oil and the steam vapor. Steam drag is causedby the relative motion between the steam and oil and the steam draggingthe oil along. Steam drive is the force created by the steam pushing theoil ahead of the steam as it moves through the reservoir.

Ref. 5 shows conclusively that the gravity drainage effect is the mostcritical factor in oil recovery in heavy oil systems undergoingdisplacement by steam.

Very few of these prior art systems have been used in the industry withany success because of their technical complexity, operationaldifficulties, and being physically impossible to implement or beingextremely uneconomical systems.

Shortcomings of prior art can be related a combination of effects. Theseinclude;

-   -   the inability of the method to inject the hot fluid into a cold        highly viscous oil in the formation;    -   the inability to overcome the viscosity effect, wherein the        viscosity of steam is less than 0.020 cp under the reservoir        conditions which makes the flow of steam through porous media        5,000,000 times easier than cold high viscosity oil of 100,000        cp. This flow ratio is based directly on the viscosity ratios of        100,000/0.02;    -   the inability of the method or process to prevent bypass of        injected fluid directly from the injector source towards the        producing sink;    -   the inability of the method or process to provide an effective        seal to prevent high pressure injected steam from bypassing cold        viscous oil impregnated formation and moving directly from the        injector source towards the producing sink;    -   the inability of the method or process to form a viable        communication zone from the steam zone or chamber to the        producing sink while preventing bypass and early breakthrough of        steam;    -   the inability of the process to utilize the significant gravity        drainage effects created by the low density of the hot steam        compared to condensed water and hot oil;    -   the inability of the method to heat the formation effectively by        physical contact between the steam and the rock formation such        that the latent heat, which the major source of heat energy        compared to the sensible heat, can be transferred to the rock        and hydrocarbons efficiently;    -   the requirement of long injection lead times of months to years        of hot fluid injection, before there is any production response        of the displaced oil;    -   the use of overly complex equipment of questionable operational        effectiveness to implement the method in the field.

For example, in U.S. Pat. No. 3,994,341, this embodiment which althoughon the surface resembles the invention herein differs significantlysince the U.S. Pat. No. 3,994,341 patent forms a vertical passage wayonly by circulating a hot fluid in the wellbore tubulars to heat thenearby formation, the 3,994,341 patent claims the drive fluid promotesthe flow of the oil by vertical displacement downwards to the producingperforations at the bottom, the U.S. Pat. No. 3,994,341 patent teachesthat the production perforations are set at the bottom of the verticalformation, a distance which can be several hundred feet. In this U.S.Pat. No. 3,994,341 embodiment, since no control mechanism like a backpressure system or pressure control system is taught, it is obvious thatthe high pressure drive steam, usually at several hundred poundspressure, will preferentially flow down the vertical passagewayimmediately on injection and bypass the cold formation with its highlyviscous crude and extremely low transmissibility. The same argument ofsteam bypass applies to U.S. Pat. No. 4,037,658 which teaches ahorizontal tube arrangement instead.

Secondly, the large distance between the top of the formation and thebottom of the formation will cause condensation of the drive steamallowing essentially hot water to be produced at the bottom with lowquality steam, both fluids being re-circulated back to the surface. Inaddition the mechanism to heat the near wellbore can only be based onconductive heat transfer through the steel casing. Since there is noformation rock contact with the steam fluid in which latent heattransfer to formation fluids and rock is the major heat transportsystem, the U.S. Pat. No. 3,994,341 method is incapable of deliveringsufficient heat in a reasonable time to heat the formation sufficientlylower the viscosity of the oil, raise the porosity and permeability ofthe formation as taught in the present patent application.

To date, the majority of producing or injection horizontal wellembodiments shown in the petroleum industry have but a single wellheadand are all limited by several physical and operational problemsassociated with the physical nature of the embodiments. This newembodiment shown herein removes many of the problems associated with theprior art.

In this new embodiment, using 3 drilling phases, a horizontal well isdrilled downward to the target formation and across the target producingformation at the required depth and at a predetermined angle and thenupward back to the surface. Inside the formation the wellbore is drilledat a slant such that the essential gravity flow component of therecovery process can be optimized. In this phase of the drillingprocess, a typical drilling plan with a conventional drilling bottomhole assembly is used. At the end of the horizontal or lateral portion,the start of the upward leg of the well is initiated. Since drilling“uphill” is operationally more difficult with heavy drill pipe andworking against gravity, a novel solution is needed. This invention alsoteaches this novel solution.

In this upward portion a smaller bottom hole assembly with a smallerdrill bit used. A small pilot hole is drilled on the upward portion toallow for operational ease and to minimize any problems in the drillingprocess. This smaller hole requires less drilling torque produces lessdrag and requires less weight on the bit. The portion is drilled in twophases. It also minimizes drilling fluid loss and any damage to the nearsurface water zones. This is one novel and innovative part of thisembodiment since the well involves drilling holes of varying diametersdrilled in two or more sequential sections in which the last section isbeing drilled upwards to the surface of the ground. In one embodimentwhen the pilot hole is completed, the upward section can be enlarged byback reaming it to a larger size by using a reamer bit that is pulledfrom the exit side backward toward the horizontal leg of the well. Thisapproach is similar to that used in river crossings in the pipe layingindustry. In another embodiment an option is to use a conventional rigand ream the hole in the usual manner by drilling forward. This sequenceof operations provides a novel approach to building the upward sectionof the well bore. In both cases the near surface groundwater must beprotected by casing put in place or by using low loss fluids during thedrilling process.

All of the prior art relates to horizontal directional drilling usedprimarily for river crossings, highway crossings involved in pipelinelaying, optical fiber laying and environmental remediation. No effort todate has used this technology effectively for oil recovery in a mannerand form such as the uniwell™ described herein.

It is seen that the above prior art techniques have several shortcomingsand disadvantages that can be avoided by the current invention whileimproving the recovery process efficiency and lowering the costs.

There is a long felt need in the industry for a means of moving theheated low viscosity crude oil that has been contacted by the steam inthe steam zone to a place or location where it can be produced withouthaving to move it through a cold heavily viscous oil impregnatedformation. This problem has continued to baffle the contemporary andprior art with possibly the only exception being the SAGD patent whichuses two horizontal wells closely juxtaposed in a vertical plane. Eventhis SAGD approach has inherent difficulties in initiating the hot oilflow between the two wellbores. Trying to push the hot oil through acold formation is an intractable proposition. The subject inventionoffers a solution to this need and provides the mechanism by which thesolution can be implemented using conventional equipment and procedures.

THIS NEW INVENTION provides an improvement in the method whereby theoperator drills a specially designed horizontal well which is drilledfrom the surface down to the producing formation and continues back upto the surface as shown in the figures herein. This continuous wellborebehaves simultaneously as both an injector and a producer. Thetechniques proposed herein uses a combination of drilling activitiesthat are known separately and distinctly in the industry, but have notyet been utilized in this integrated manner shown in this new invention.

THIS INVENTION allows the operator to rapidly drill a specializedhorizontal well to the producing formation which allows efficientrecovery of heavy oil from the subterranean formation. This new drillingtechnology can be applied to the following systems; heavy oil deposits,tar sands and oil shale systems.

THIS INVENTION allows the orderly development of oil reserves,especially heavy oil reserves by allowing the efficient and costeffective production of these deposits.

SUMMARY OF THE INVENTION

An object of this invention is to provide an improved method forrecovery of oils from subterranean formations by exploiting theadvantages provided by gravity drainage in the displacement process ofheavy oils in porous formations using steam or combustion drivendisplacement processes. The use of a single modified well bore, with adownward, lateral and upward section, the uniwell™, has severalengineering benefits including cost reduction, better fluid displacementand more engineering control of the injection and oil recovery process.

The invention presented herein utilizes two of the three components onsteam displacement discussed in the prior art. These are gravitydrainage and steam drive. There is very little relative motion betweenthe steam and the oil so there is very little steam drag if any at allin this invention.

A more specific objective is to provide an improved means of drilling aproducing wellbore in subterranean formations by using a sequentialdrilling method to build and drill the upward portion of the well afterthe lateral portion is drilled.

Another specific objective is to provide a means by which theoperational difficulties created by using heavy drill pipe and drilling“uphill” can be overcome. The drilling of the upward portion of thewellbore is implemented by using a pilot hole, a new oilfield concept,in which a small pilot hole is drilled upwards with a very smalldrilling assembly and bit and then the bore of this section can beenlarged afterwards.

Another specific objective is to provide a means for enlarging theupward section of the wellbore by using a back reaming process with aback reaming bit from the exit end to the horizontal lateral.

Another specific objective is to provide a means for enlarging theupward section of the wellbore by using a forward reaming process fromthe exit end to the horizontal lateral by using a typical conventionaldrilling rig with a forward drilling reaming bit.

Another specific objective is to provide for maximum gravity drainageduring oil production by drilling the lateral portion at an angleselected to maximize oil production while allowing maximum steam effecton the formation during steam recovery processes.

Another specific objective is to provide a means whereby the lateralportion of the uniwell™ can be extended below the target oil zone toallow maximum contact and drainage within the oil zone of the injectedsteam and still provide the necessary gradient needed for gravitydrainage of heated oil.

Another specific objective is to provide a means where the upwardportion of the uniwell™ can begin below the oil zone and be extendedupwards to the surface to accommodate the extended lateral wellbore asdescribed above.

Another specific objective is to provide a means whereby the samewellbore perforations along the horizontal section of the wellbore canbe used sequentially for either injection or production as required bythe operator.

Another specific objective is to use the movable packer between theinjection and production perforations, which forces the steam to exitthe wellbore and enter the oil zone at a preset location upstream of theproduction perforations.

Another specific objective is after the initial oil region is depleted,to unseat and move the movable packer between the injection andproduction perforations a preset distance along the axis of the wellboreand reseat it to allow the steam displacement process to continuethroughout the reservoir in a new undepleted oil zone.

Another specific objective is to provide a means to considerably reducethe distance the heated oil has to move from the steam injection pointto be produced in the wellbore through the producing formations.

Another specific objective is to provide a concentric communicationchannel in the formation, which allows the heated oil to move from theupper steam zone to the perforations in the lower production zone.

Another specific objective is to provide a means whereby oil productionbegins as early as possible during the injection process compared toexisting technologies like Steam Assisted Gravity Drainage (SAGD) andconventional Thermal Enhanced Oil Recovery (TEOR).

Another specific objective is to minimize the need to preheat theproducing elements of the wellbore and the near wellbore region for along time to raise the temperature and to lower oil viscosity in orderto initiate oil production into the cold producer region.

Another specific objective is to maximize steam zone growth by keepingthe steam vertically isolated and higher within the oil formation thusallowing greater steam growth and less potential for steam breakthrough.

Another specific objective is to allow the steam to replace oil and topressure up the steam bank at the top, which helps to displace lowviscosity, heated oil downwards along the interface of steam/coldreservoir oil to the producing perforations where there exists apressure sink because oil is being removed during production.

Another specific objective is to minimize the effects of a bottom waterdrive on degrading the steam efficiency since the short distance betweensteam and oil production perforations allows steam to maintain contactwith new oil and not be diffused into the bottom water and dissipate itsheat content to the higher heat capacity interstitial water.

Another specific objective is to allow the horizontal wellbore to bedrilled close to the bottom of the formation where a water zone existsby making the perforations on the upper side of the lateral wellboreusing specialized perforating techniques available in the industry. Thisallows the injected steam to enter the oil zone preferentially and tostay out of the bottom water zone, while the hot produced oil can beproduced from the perforations downstream of the injector point.

Another specific objective is to preclude the need for two wellbores inthe same vertical plane, to recover oil as shown in some conventionalSAGD technologies, since in thin zones, it is impossible to successfullydrill two workable oil wells within the same thin zone using existingdrilling equipment.

Another specific objective is to overcome the need for two verticallyseparated wellbores within close tolerances as proposed in SAGD which isexpensive and depends on critical placement of two wells within avertical axis of 2 meters or less to guarantee hot oil dripping from thetop well will not bypass the bottom well.

Another specific objective is to allow the steam to be injected in ahorizontal or planar manner into the reservoir. This planar flow fromthe horizontal axis of the wellbore creates smaller pressure gradientsas opposed to pure radial flow in the customary steam injection process.

Another specific objective is to create smaller pressure gradients bythe inward horizontal flow along a significant wellbore distance duringthe production phase and therefore lower the possibility of coning offluids, in this case steam and formation water. The coning of steamand/or water is an unwanted condition in this type of recovery systemsince it wastes energy and produces water that replaces oil.

Another specific objective is to drill the wellbore with differentdiameters in different sections particularly in the lateral portion andthe upward leg to minimize costs, increase production and control wellbore location.

Another specific objective is to use the accumulated oil in the lateraland upward portion of the wellbore to act as an U-tube device, whichbehaves similarly to a P-trap in a household drain, allowing the steamto remain on the injector side of the wellbore and maximize growth ofthe steam zone in the reservoir where it is more effective.

Another specific objective is to use the produced oil, which accumulatesin the lateral and upward portion of the wellbore to act as abackpressure system such that the steam bank is prevented from breakthrough by flowing down the wellbore.

Another specific objective is to use the bottom hole pump and bycontrolling surface production rates thereby allowing the reservoirpressure to be maintained at a level such that no steam is producedbecause of the back pressure in the production wellbore.

Another specific objective is to use the slim-hole drilling in theupward portion of the wellbore to minimize damage to near surface waterzones on the “punch-out” or exit side of the wellbore since drillingoccurs through a small rock volume limiting the potential for surfacezone damages.

Another specific objective is to use the slim-hole drilling in theupward portion of the wellbore to minimize damage to near surface waterzones since the drilling time is very short and fluid loss during theshort time is minimized.

Another specific objective is to use a plurality of parallel uniwells™simultaneously over a large areal extent to maximize reservoir recoveryby minimizing the heat losses laterally from a single uniwell™ and toprovide a steam drive process that increases production by literallyhaving a steam front move through the reservoir as a vertical plane.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention consists of the wellbore and associated componentsshown in the figures below:

FIG. 1 Shows an overview of the uniwell™, with the downward, thehorizontal lateral and the upward sections of the wellbore.

FIG. 2 Shows the completed downward and lateral portion of the uniwell™with the initiation of the pilot hole using a smaller bottom-holedrilling assembly.

FIG. 3 Shows the completion of the pilot hole.

FIG. 4 Shows and the initiation of the back reaming process to enlargethe pilot hole.

FIG. 5 Shows and the initiation of the forward reaming process toenlarge the pilot hole.

FIG. 6 Shows the extension of the lateral section of the wellbore belowthe oil zone and into the under-burden to allow maximum contact of steamin the oil zone. Also shown is upward section.

FIG. 7 Shows a field use of the embodiment in steam recovery of heavyoil.

FIG. 8 Shows a field use of the embodiment in an in-situ combustionrecovery of heavy oil or tar sands.

FIG. 9 Shows the flow lines in plan view of a single uniwell™ during asequence of operational phases in which the movable packer is unseated,moved and re-seated after local oil depletion occurs.

FIG. 10 Shows a plurality of uniwells™ located in parallel in areservoir system.

FIG. 11 Shows initial heating of the near wellbore zone to allowcommunication pathway for heated oil. This is done by a removabledownhole heater or less effectively by circulating a hot fluid likesteam.

FIG. 12 Shows the reamed out open-hole zone which is concentric to thewellbore and used for hot oil communication from the injection zonesteam bank to the production perforations.

FIG. 13 Shows a block diagram of the operational aspects of theinvention.

FIG. 14 Shows a block diagram continuing the operational aspects of theinvention.

FIG. 15 Shows a block diagram continuing the operational aspects of theinvention.

FIG. 16 Shows the graph of production during a typical operation of theprior art in which a “huff and puff” steam field operation isimplemented.

FIG. 17 Shows the graph of the almost continuous steam injectionoperations implemented in this invention, with the non-injection periodsfor wellbore annulus heating and moving of retractable packers.

FIG. 18 Shows the on-off oil production graph in a more detailed versionof a part of the production cycle early in the life of the fieldoperations.

FIG. 19 Shows the graph of the growth trend in oil production rates asthe steam injection continues followed by the natural declineaccompanying oil reserves depletion. Item No. Description of Elements  1Uniwell Wellbore  2 Underburden Formations  3 Overburden Formations  4Entry wellhead on input side.  5 Exit wellhead on punch-out side.  6Downward section of horizontal well bore  7 Lateral or horizontalsection of wellbore  8 Completed upward section of horizontal wellbore 9 Surface of ground 10 Kick off point for start of curved portion ofwellbore 11 Drilling Assembly 12 Pilot Hole 13 Upward section ofhorizontal wellbore after pilot drilling 14 Back reamer Bit 15 EnlargedWellbore of upward section 16 Drill Pipe 17 Pull back drill rig used inback reaming process 18 Drill rig used in forward reaming process 19Drill Pipe used in forward reaming process 20 Forward Reaming Bit 21Overshoot Extension of lateral into underburden 22 Direction of BitTravel 23 Subterranean Oil Zone 24 Downhole Pump 25 Casing Tubular pipe26 Liner tubular pipe 27a Perforations for injection 27b Perforationsfor production 28 Drilling Rig 29 Moveable Oilfield Packer 30 InjectedSteam Zone or Steam Bank 31 Hot oil flow direction 32 Parallel wellbores33 Injected gases for combustion front 34 Burned zone behind combustionfront 35 Combustion Front 36 Zone of vaporized oil 37 Light HydrocarbonZone 38 Hot Produced Oil 39 Downhole Heater 40 Power Cable to Heater 41Annular steamed communications zone 42 Reamed out annular zone 43Hydraulic P-Trap effect 44 Steam injection time. 45 Steam soak time 46Oil production rate decline curve 47a Oil production cycle period. 47bOil daily production rate 47c Well Shut-in period, zero production rate48 Wellbore heating period. 49 Oil flow rate increase trend 50 Oil flowrate decreasing trend.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT:

Referring now to the drawings wherein like reference numerals designatecorresponding elements throughout all the figures and referring inparticular to FIG. 1. an improved method for extracting hydrocarbonsaccording to an example embodiment of the invention includes a wellbore1 consisting of three primary sections. As shown in steps 100, 101, 102,in FIG. 13 and in FIG. 1, a downward section 6, a lateral section 7 andan upward section 8 are drilled with conventional oilfield equipment.The downward section 6 has an entry wellhead 4 and is more or lessvertically drilled depending on the nature of the recovery operations.Within the scope of this description a horizontal well or horizontalwell section means a well or well section, which is substantially at orclose to horizontal inclination. The horizontal or lateral section 7 isdrilled in the producing oil formation 23, which is a porous mediumcontaining oil, gas and water in the pore spaces. The upward section 8is a continuation of the lateral section 7 upward along a predeterminedcurve to the surface 9. A steel casing 25 or steel liner 26 depending onthe type of well and the location within the formation can line thewellbore 1. In other embodiments an “open-hole” completion can be usedin which there is no steel casing. This can be done in well consolidatedrock formations. At the entry end of the well 1 there is an entrywellhead 4 and an exit wellhead 5 is on the distal end.

Perforations 27 b, 27 a are made in the casing to allow oil to beproduced or in the case of injection operations to allow injected fluidsto enter the oil zone 23. The oil zone 23 is overlain by an overburden 3and under-burden zone 2. These zones are impermeable and trap thehydrocarbons in the oil zone 23 and from which oil production ispossible when the well 1 drilled into the oil zone.

Referring to FIG. 2, a drilling assembly 11 is used to drill through theformations. This assembly is connected to the drill rig 28 at thesurface by a drill pipe 16. In some cases the bottom hole assemblyconsists of a downhole motor and a drill bit. In other cases coiledtubing can be used instead of drill pipe. All the drilling practices arewell known in the industry and are not part of this invention. The pointwhere the vertical hole section 6 changes to a horizontal section 7 iscalled the kickoff point 10. Referring to FIG. 3, a small pilot hole 12is that portion of wellbore 12, which extends from the lateral section 7to the surface 9 along a predetermined path 13.

Referring to FIG. 4, the back reaming process shown in step 101 isimplemented, using the back-reamer bit 14 which travels through thepilot hole 12. The bit 14 is pulled backwards by pull back drill rig 17at surface 9 using the drill pipe 16. The enlarged hole 15 developsbehind the reamer bit 14. Referring to FIG. 5, a forward reaming processis subsequently implemented by using the forward reamer bit 20 isconnected to the drill rig 18 at the exit end 5 by drill pipe 19. Thereamer bit 20 moves in a forward direction 22 as it moves down the pilothole 12 while the rig 18 rotates the reamer bit 20. In FIG. 6, thelateral section 7 can be extended 21 below the oil zone 23 and into theunder-burden 2 in order to extend the range of the well and allow moregravity effect on production in the vertical direction. A downhole pump24 is shown in this embodiment. The pump is used to lift the producedfluids to the surface as needed.

FIG. 7 shows an embodiment of the invention for steam recovery of heavyoil. In a conventional steam recovery process, steam usually generatedon the surface using combustion boilers or as a by product of a electricpower cogeneration operation, is injected into the injector wellbore toheat the heavy oil, decrease its viscosity and drive it towards aproducer well some distance away from the injector. Referring to FIG.11, as indicated in steps 103 and 104 b of FIG. 13 in this embodiment, adownhole heater 39 is used to conductively preheat a near wellboreannular region 41 to a relatively high temperature of several hundreddegrees Fahrenheit between 300 F and 700 F, in a short time. Thistemperature is sufficient to increase the rock permeability, lower thein-situ hydrocarbon viscosity significantly, raise the rock porosity andincrease the oil saturation in the heated zone. After this preheatoperation is implemented for a sufficient period of time, the downholeheater is removed. Referring to FIG. 7, in this embodiment, steam 30 isinjected into the oil zone 23 through perforations 27 a which arestrategically placed in the well casing 25. As indicated in step 105 thesteam is prevented from traveling down the wellbore by a movable packer29, which separates the steam injector section from the oil productionsection. In an “open hole” completion, this packer 29 can be aretractable inflatable packer in those situations where the well iscompleted without a casing 25. This blocking packer is retracted andmoved along the axis of the lateral 1 as the steam zones are depletedand new oil production occurs as the processes are repeated.

During the recovery process, the steam forms a zone or steam bank 30 inwhich oil is heated creating a tremendous drop in viscosity allowing theoil to flow easier. A viscosity drop from 10,000 cp at reservoirconditions to 2 cp at steam conditions is possible. The annular regionpre-heated in step 104 b by the downhole heater provides a highconductivity communication path 41 and driven by gravity and otherhydraulic forces, the hot low-viscosity oil 38 moves to the lowerdownstream perforations 27 b as shown in step 108 of FIG. 14. As hot oil38 accumulates in the lateral section 7 and fills the wellbore, itprovides a hydraulic “P-trap” effect 43 shown in FIG. 6, which acts as abackpressure valve preventing the bypass of steam from the upperperforations 27 a to the lower perforations 27 b. In one embodiment, thewellbore segment liquid can be pressured from the surface with naturalgas or some inert gas to help implement the “P-trap” effectpneumatically in addition to hydraulically. As indicated in step 109 ofFIG. 14, by modulating production rates a process called “choking” inthe industry, this backpressure can be used to minimize and prevent anysteam bypass in step 110. Oil is produced with a pump 24 if the pressureis insufficient to flow to the surface or it can flow to the surface ifthe driving pressure is sufficiently high. As can be seen from thephysical implementation of this new embodiment the heated oil 38 travelsonly a few feet, a significantly shorter distance in the steam zone 31to the producing perforations 27 b. This compares to the very largeinter-well distances of several hundred feet, through cold highlyviscous oil zones with limited transmissibility that the hot oil has totravel in conventional steam floods as shown in Ref. 3. The newembodiment shown herein allows oil recovery to begin almostinstantaneously via the highly communicative annular zone developed bythe preheat process described above. This is in stark comparison to thelong steam injection and steam soak times needed for the conventionalsteam flood to displace oil to the producer well.

Referring to FIG. 8 which shows an embodiment of the invention inin-situ combustion recovery of heavy oils or tar sands also called afireflood. In this embodiment, a downhole heater 39 is used toconductively preheat a near wellbore annular region 41. After thispreheat the downhole heater is removed. Air 33 is then injected down thedownward section 6 of the uniwell™ through perforations 27 a and intothe oil zone 23. Following the operations of a typical fireflood acombustion front 35 is initiated in step 107 a. This burning front 35creates a zone of vapors 36 and a zone of light hydrocarbons 37 ahead ofthe combustion front. In the conventional fireflood, the intent is toheat the oil to drop the viscosity and move the free flowing oil towardsthe producer wellbore several hundred feet distance away. In thisembodiment as the combustion front moves forward through the reservoir,the heated oil 38 decreases in viscosity and it flows downwards undergravity and other physical forces to the wellbore 1 and through thehighly permeable annular communication zone 41 and enters through theperforations 27 b. As can be seen from the physical implementation ofthe embodiment the heated oil travels a significantly shorter distancefrom the combustion zone 35 to the producing perforations 27 b and notneeding to flow through a cold formation. This compares to the verylarge inter-well distances through cold highly viscous oil zones withlimited transmissibility, that the front has to travel in conventionalcombustion floods as shown in Ref. 3. The new embodiment shown hereinallows oil recovery to begin almost instantaneously compared to the longcombustion times needed for the conventional fireflood to displace oilto the producer well. Oil recovery begins in days via the highlycommunicative annular zone developed by the early preheat process,rather than in months and years under conventional combustion processesand this time shortened time factor increases the economic viability andprofitability of the overall process.

Referring to FIG. 9 a plan view of an embodiment is shown in which twocycles of injection and production are superimposed. The first cycleshow the stream flow lines 30 from steam injected into the wellboreperforations 27 a and the oil produced from the wellbore perforations 27b. After a prescribed time interval, the downhole packer 29 is moveddown from position ‘a’ to position ‘b’ in the wellbore between the nextset of injection and production perforations. A new cycle of operationsis initiated as shown in FIG. 15, steps 113, 114, 115 a, 115 b and 116.The downhole heater 39 is re-installed and the new wellbore annular zoneis heated to provide a high conductivity zone for hot fluid movement.Next the first production perforation is converted to steam injectionand the oil is produced into the wellbore from the next perforation setalong the axis of the lateral wellbore. The stream flow lines 31 areshown in the figure. Continued steam injection can still occur in thefirst set of steam perforations or they can be plugged off if needed toallow the steam front to advance more rapidly.

Referring to FIG. 10 a plurality of parallel wellbores 32 used in anembodiment is shown. This parallel approach allows a planar displacementof oil by the injected steam as injection continues into the reservoir.

Referring to FIG. 11 the initiation of a flow channel 41 is shown. It ismade by initially heating the area around the lateral wellbore 7 byusing a removable downhole heater 39 which heats the rock to between 300F and 700 F. This heating lowers the oil viscosity, increases the rockporosity and permeability and lowers the water saturation in the nearwellbore region opposite the downhole heater. It is possible but notnearly as effective to form the communication zone by injecting steamfor a few days through the first sets of injectors to allow the zonearound the wellbore to be heated and to lower the viscosity of oil inplace in this near wellbore region.

Referring to FIG. 12 which shows another embodiment of the invention inwhich a section of the lateral wellbore 7 is reamed out in step 104 aduring the drilling process to make a large open-hole annular zonesection 42. This annular cylinder 42 around the wellbore forms thecommunication zone through which the produced fluids 38 move from thesteam zone 30 to the production zone. The steam is injected down thewellbore 6, the wellbore packer 29 diverts the steam into the coldformation 23 where a steam chamber 30 develops. The formation oil isheated by the steam and flows down the sides and periphery walls of thesteam chamber under gravity towards the bottom of the steam chamber. Theproduced oil and condensed steam flow down the reamed out zone 42towards the bottom of the wellbore. In this embodiment the producedfluids accumulate in the lateral wellbore 7 and fill the productionstring.

A novel aspect of this invention is the use of the heated oil in thewellbore sections to act as a hydraulic pressure control and a flowcontrol device. By modulating the production of the fluid produced theprocess creates a back pressure and a fluid “P-trap” seal in the lateralsection of the wellbore which prevents the injected steam from bypassingthe cold formation and forcing the steam to remain in the steam bankzone and then to grow vertically.

Operationally the drilling operation is summarized as follows; thedownward portion 6 is drilled in a conventional manner, at the kickoffpoint 10 the lateral portion 7 is drilled using the typical horizontaldrilling operations found in the oilfield today. At the start of theupward portion 8, the drilling assembly is changed to allow the processto continue less expensively with a slim hole assembly 11, which employsa smaller bit to drill the pilot hole to the surface along a plannedtrajectory 12. On reaching the exit end on the surface the pilot hole 12is reamed out to a larger size by either a back reamer 14 or by using aforward reamer bit 20. The extension 21 of the lateral below the oilzone 23 is a simple modification of the basic drilling process. In asimilar manner the completion processes which include cementing ofcasings, perforating of casings, or setting of liners in the wellbore,installing of pumps and valves are basic processes in the oil drillingindustry and are well known to all versed in the art.

In engineering the steam injection operation, a computer or simulationanalysis is routinely used in the industry to calculate the optimalrequired injection time of steam into the hydrocarbon bearing formationfor optimal oil recovery. This analysis incorporates steam flow rate,steam quality, steam pressure, formation rock properties, oil saturationand depth of formation from the surface.

In this invention, during the earliest steam injection time only, theproduction of hot oil is maintained at zero to allow the oil toaccumulate in (a) the bottom of the steam bank, (b) in the verticalcommunication zone and (c) in the wellbore segment. This accumulated hotoil behaves as a hydraulic seal preventing steam from bypassing theformation and flowing into the wellbore. In alternative embodiments, thebackpressure system described herein prevents the production of oil intothe wellbore. These no-flow embodiments are essential and by preventingoil flow, they allow a steam bank to grow since the injected steam isforced to enter the formation directly heating the rock and in-situhydrocarbons.

After the requisite injection time, which is nominally a matter of days,the production of hot oil and condensed water is initiated by permittingthe removal of hot fluids from the wellbore via the production system orby lowering the backpressure on the fluid column in the wellbore. Afterthe production of accumulated hot oil is complete as evidenced by theincipient flow of dry steam detectable at the surface, the fluidproduction is shut down and the accumulation of hot oil and condensedwater at the bottom of the steam bank resumes. It should be noted thatin this invention, except as noted later, steam injection is acontinuous operation and the oil production phase is started and stoppedat specific operational conditions during this thermal recovery process.

This invention differs significantly from the prior art in itsimplementation in the field. The ability of the well to be produced verysoon after steam injection begins, allows oil revenue to begin almostimmediately. Furthermore the volumetric flow rate of oil remainsrelatively constant while the steam bank is growing and can evenincrease as cumulative steam injection occurs. This is due to the largervolume of rock being contacted and heated thus lowering the oilviscosity and also by increasing the vertical extent of the steam bank,the gravity effect on the oil flow column is increased, both resultscontribute to increased oil flow rates.

A typical response of a steam heated heavy oil reservoir using the priorart of huff and puff operations is shown in FIG. 16. It should be notedthat after the steam injection time 44, steam injection is curtailed andafter the soak time 45, the well is put on production as shown in curveelement 46. There is an initial increase in oil production rate whichimmediately declines exponentially to the un-stimulated level after anumber of days. This process is repeated several times to fully developthe steam operations and deplete the oil reservoir.

On the other hand, the invention described herein, provides for a verydifferent set of operations. FIG. 17 shows the steam injection period 44followed by the period 48 in one embodiment in which the wellbore heater39 is installed in the wellbore and is operated for a fixed time, andduring which time the packer 29 is also moved along the wellbore. Notethat the steam injection rate is essentially constant, however inpractice it is usually necessary to increase the injection rate overtime to offset the heat losses as the steam bank increases in size.

FIG. 18 shows a more detailed set of operational data where the wellproduction is intermittent. This occurs early in the steam operationssince the steam zone or steam bank 30 is still small and growing and theaccumulated oil 38 is insufficient to be produced continuously withoutcompromising the hydraulic seal 43 and allowing steam breakthrough inthe communication zone 41 and the wellbore 1. This figure shows the oilproduction rate 47 b and the oil shut-in period 47 c.

As the steam bank 30 grows, there is more reservoir formation 23 volumeavailable for oil production and there is a concurrent increase in theoil production rate as shown by the trend line 49 in FIG. 19. This trendcontinues to a maximum point after which there is an inevitable declinedue to heat losses, oil depletion and other factors as shown by trendline 50.

Given the increased oil flow rates which begin soon after steaminjection, coupled with the growth of the steam bank by almostcontinuous steam injection, as opposed to the intermittent injection ofthe prior art huff and puff method; and the concurrent oil productionincrease, this invention provides for an improvement in the technologyand prior art in a manner which allows significant rapid development ofhydrocarbon reserves from heavy and viscous oil from subterraneanformations with existing equipment and field operations applied in amanner that has been heretofore lacking.

Various modifications and alterations of this invention will becomeapparent to those skilled in the art without departing from the scopeand spirit of this invention and it should be understood that thisinvention in not unduly limited to that set forth herein forillustrative purposes.

In this patent certain U.S. patents, patent applications, and othermaterials (e.g., articles) have been incorporated by reference. The textof such U.S. patents, U.S. patent applications, and other materials is,however, only incorporated by reference to the extent that no conflictexists between such text and the other statements and drawings set forthherein. In the event of such conflict, then any such conflicting text insuch incorporated by reference U.S. patents, U.S. patent applications,and other materials is specifically not incorporated by reference inthis patent

Further modifications and alternative embodiments of various aspects ofthe invention may be apparent to those skilled in the art in view ofthis description. Accordingly, this description is to be construed asillustrative only and is for the purpose of teaching those skilled inthe art the general manner of carrying out the invention. It is to beunderstood that the forms of the invention shown and described hereinare to be taken as the presently preferred embodiments. Elements andmaterials may be substituted for those illustrated and described herein,parts and processes may be reversed, and certain features of theinvention may be utilized independently, all as would be apparent to oneskilled in the art after having the benefit of this description of theinvention. Changes may be made in the elements described herein withoutdeparting from the spirit and scope of the invention as described in theclaims.

References:

1 Robbins Horizontal Drilling, 29100 Hall St, Solon, Ohio 44139.www.robbinstbm.com

2. The Crossing Company Inc.,1807-8th Street, Nisku, Alberta, Canada T9E7S8, www.thecrossingcompany.com

3. Improved Oil Recovery—Exxon Background Series (1982), NY. NY 10020.

4. The Society of Petroleum Engineers 222 Palisades Creek Dr.,Richardson, Tex. 75080, U.S.A. www.spe.org.

5. “A Comparison of Mass Rate and Steam Quality Reductions to OptimizeSteamflood Performance”, Topical Report 108, Gregory L. Messner, July1998, Stanford University, Stanford, Calif.

1. A method for recovering hydrocarbons from a subterranean formationcontaining viscous oil or other heavy hydrocarbons; the methodcomprising the steps of: (a) drilling at least one wellbore comprising avertically drilled downward section, a lateral section and an upwardsection, in the hydrocarbon bearing formation by penetrating theformation with conventional drilling equipment; (b) providing a wellheadat the entrance or proximal end of the wellbore and another wellhead atthe exit or distal end of the wellbore; (c) providing a plurality ofperforations in the wellbore at pre-selected intervals; (d) installing adownhole wellbore packer between upper and lower perforations; (e)forming an annular hot zone of increased fluid conductivity near thesaid wellbore in the said formation to facilitate vertical flow ofheated low viscosity oil and hot water produced from condensed steam,towards lower production perforations; (f) heating the said formation byinjecting a displacing fluid into the formation; (g) lifting theproduced oil and displaced fluids to the surface.
 2. The method of claim1, wherein the said formation is heated by injecting steam through upperperforations as a displacing fluid.
 3. The method of claim 2, whereinthe injected steam heats the wellbore and surrounding formation forsufficient time and at a calculated temperature.
 4. The method of claim1, wherein the said hot annular zone is formed by installing andinitiating a downhole heater for a predetermined time greater than 24hours, and at a predetermined temperature.
 5. The method of claim 1,wherein the said formation is heated by transmitting heat energy to thesaid formation by using a combustion front.
 6. The method of claim 1,wherein the said formation is heated by transmitting heat energy to thesaid formation by using a steam chamber or steam bank.
 7. The method ofclaim 1, wherein the driving pressure of produced oil and displacedfluids is sufficiently high to push the produced oil and displacedfluids to the surface.
 8. The method of claim 1, further comprising thesteps of: installing a fluid recovery system to lift the produced oiland displaced fluids to the surface, wherein the produced oil anddisplaced fluids are lifted to the surface by using the said fluidrecovery system.
 9. The method of claim 8, wherein the said fluidrecovery system comprises a production pump.
 10. The method of claim 1,wherein the step of drilling the upward section of the wellborecomprises the steps of: drilling a small pilot hole upwards to the exitend of the wellbore with a small drilling assembly and bit; andenlarging the upward section of the said wellbore.
 11. The method ofclaim 10, wherein the step of enlarging the upward section comprises thesteps of: installing a back-reamer bit, connected to the pull back drillrig at the entrance of the wellbore by a drill pipe; and pulling thesaid back-reamer bit to travel from the exit end of the wellbore throughthe small pilot hole to the entrance, to enlarge the upward section ofthe said wellbore.
 12. The method of claim 10, wherein the step ofenlarging the upward section comprises the steps of: installing aforward-reamer bit, connected to the drill rig at the exit end of thewellbore by a drill pipe; and rotating the said forward-reamer bit andpushing it forward to travel from the exit end of the wellbore throughthe small pilot hole to the entrance, to enlarge the upward section ofthe said wellbore
 13. The method of claim 1, further comprising the stepof cementing a steel casing in the wellbore in the said formation. 14.The method of claim 1, wherein the wellhead at the proximal end of thewellbore is an injection wellhead.
 15. The method of claim 1, whereinthe wellhead at the distal end of the wellbore is a production wellhead.16. The method of claim 1, wherein the perforation zones in the wellboreare positioned as paired groups or couplets.
 17. The method of claim 16,wherein the proximal perforations in the pair group form an injector setof perforations.
 18. The method of claim 16, wherein the next or distalset of perforations in the pair group forms a producer set ofperforations.
 19. The method of claim 1, wherein the downhole packer inthe wellbore is placed between the injector and producer pair ofperforations separating the injection and production zones.
 20. Themethod of claim 1, wherein the downhole packer forces the injectionfluid to be to exit the wellbore and be injected into the hydrocarbonbearing formation.
 21. The method of claim 1, wherein the downholepacker is retractable and be either solid or inflatable.
 22. The methodof claim 1, wherein the injected fluid is steam.
 23. The method of claim1, wherein the injected fluid forms a steam bank or chamber in thehydrocarbon reservoir.
 24. The method of claim 1, wherein the said hotannular zone is formed by installing a reaming device and reaming out aportion of the said formation, thereby enlarging the said wellboresubstantially.
 25. The method of claim 24, wherein the reamed zone isconcentric to the wellbore.
 26. The method of claim 24, wherein thereamed zone forms an axial communication zone for fluid flow from thesteam bank to the production zone perforations.
 27. The method of claim1, wherein the downhole packer is moved axially along the wellbore tonew hydrocarbon rich formations to carry out the said method, after eachsteam displacing zone is depleted of hydrocarbons.
 28. The method ofclaim 1, further comprising the step of: installing a downholebackpressure valve in the said wellbore to create a backpressure toprevent the injected steam from bypassing downwards into the productionperforations.
 29. The method of claim 1, wherein the accumulation ofproduced hot oil in the lateral section is controlled by controlling thefluid production rate at the distal end of the wellbore, to provide ahydraulic “P-trap” effect, which acts as a backpressure valve preventingthe bypass of steam from the upper perforations to the lowerperforations.
 30. The method of claim 29, wherein the said wellbore ispressured from the surface with natural gas or some inert gas toimplement the “P-trap” effect pneumatically in addition tohydraulically.
 31. The method of claim 1, wherein the injected fluid isair.
 32. The method of claim 1, wherein the injected fluid is acombination of steam and heated water.
 33. The method of claim 31,wherein the injected air provides the oxygen needed for combustion frontof the in-situ hydrocarbon.
 34. The method of claim 1, wherein the angleof the lateral section of the wellbore in the formation ranges betweenzero (0) degrees to 90 degrees from the horizontal.
 35. The method ofclaim 4, wherein the downhole heater remains in place substantially longenough to heat radially, a preferred annular distance of at least twofeet around the wellbore.
 36. The method of claim 4, wherein thedownhole heater is retractable and moveable.
 37. The method of claim 1,wherein the heating of the annular communication zone increases theporosity of the reservoir formation in the annular region.
 38. Themethod of claim 1, wherein the selective heating of the annularcommunication region increases the permeability of the reservoirformation in the communication zone.
 39. The method of claim 1, whereinthe selective heating of the annular communication region decreases thewater saturation of the reservoir formation in the communication zone.40. The method of claim 37, wherein the increased reservoir rockformation porosity increases the fluid transmissibility of the rock tooil flow in the annular communication zone.
 41. The method of claim 38,wherein the increased reservoir rock formation permeability increasesthe fluid transmissibility of the rock to oil flow in the annularcommunication zone.
 42. The method of claim 39, wherein the decreasedreservoir rock formation water saturation increases the fluidtransmissibility of the rock to oil flow in the annular communicationzone.
 43. The method of claim 1, wherein the lateral wellbore sectionextends substantially below the hydrocarbon formation.
 44. The method ofclaim 29, wherein the P-trap is used for controlling the flow ofproduced oil in the wellbore.
 45. The method of claim 1, wherein thedisplacing fluid is injected intermittently.
 46. The method of claim 1,wherein the displacing fluid is injected continuously.
 47. The method ofclaim 1, wherein the produced fluids are recovered intermittently. 48.The method of claim 1, wherein the produced fluids are recoveredcontinuously.
 49. The method of claim 19, wherein the downholeretractable packer completely separates the injection perforations fromthe production perforation in the wellbore.
 50. The method of claim 1,wherein the heated annular zone extends substantially from below thebase of the injection perforations to the top of the productionperforations
 51. The method of claim 1, wherein maintaining a prescribedoil level in the wellbore controls the vertical steam flow.
 52. Themethod of claim 51, wherein maintaining a prescribed oil level in thewellbore prevents the flow of steam bypassing the cold formation andflowing to the production perforations.
 53. The method of claim 1,comprising a plurality of parallel wellbores simultaneously over a largeareal extent to maximize oil recovery by minimizing the heat lossesattributed to each wellbore.
 54. The method of claim 4, wherein the saidtemperature ranges between 300 deg. F and 600 deg. F.
 55. The method ofclaim 3, wherein steam is injected until the formation is depleted ofmovable oil.
 56. The method of claim 3, wherein the injected steam heatsthe formation to a temperature above 212 deg. F.